The present invention relates generally to current sensing devices for electrical systems, and more particularly to fault indicators for alternating current power systems that are capable of automatically configuring to an overhead application or to an underground application.
Various types of self-powered fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems and derive their operating power from inductive and/or capacitive coupling to the monitored conductor; and test point type fault indicators, which are mounted over test points on cables or associated connectors of the systems and derive their operating power from capacitive coupling to the monitored conductor.
Other prior art fault indicators may be either of the manually resetting type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,456,873, 4,458,198, 4,495,489, 4,974,329, 5,677,678, 6,016,105, 6,133,723 and 6,133,724.
Detection of fault currents in a monitored conductor by a prior art fault indicator is typically accomplished by magnetic switch means, such as by a configured magnetic reed switch, in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the magnetic switch actuates a trip circuit that produces current flow in a trip winding to position an indicator flag visible from the exterior of the indicator to a trip or fault indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the target indicator to a reset or non-fault indicating position, or the fault indicator may be manually reset.
Rather than a target indicator, some prior art fault indicators utilize light emitting diodes (LEDs) to display a fault condition. Whether of the target or LED display type, prior art fault indicators are typically configured for either overhead or for underground applications. This means that a variety of fault indicators must be manufactured, inventoried and sold to satisfy each specific application. Customers must also be careful that the installation of a fault indicator on a power line is of the appropriate configuration for the application. Otherwise, it can be expected that a fault indicator that is configured for an overhead application may not perform correctly or adequately in an underground application, and vice versa.
There is therefore a need for a fault indicator that can automatically determine whether it is installed in an overhead or an underground application, and that can automatically configure itself for the specific application.
There is a further need for such a fault indicator that is normally in an energy conservation mode and that periodically wakes up to monitor the load conditions on the monitored conductor, or is awakened when a fault condition occurs, when the fault indicator is reset after a timed reset period, or when a microcontroller in the fault detector otherwise receives an input or interrupt signal.
The need also arises for a such a fault indicator that will continue to display a prior fault condition for a predetermined amount of time, such as in the range of one hour to twenty-four hours, rather than self-resetting upon restoration of current in the conductor. Such timed reset fault indicators should be capable of self-resetting after termination of the predetermined time.
Some applications also require voltage in-rush restraint and/or current in-rush restraint to prevent false tripping due to a subsequent current inrush, such as when a reclosing relay of a power distribution system closes.
Because of the compact construction and limited power available in self-powered fault indicators, it is preferable that the desired functions of the fault indicator be accomplished with minimal structure and with internal circuitry that has minimal current drain on a high capacity battery. The fault indicator must also provide highly reliable and extended operation over a number of years.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator that, upon installation on a conductor to be monitored, can automatically determine whether it is in an overhead or underground application.
Another object of the present invention is to provide such a fault indicator that can automatically configure itself for the overhead or underground application.
Yet another object of the present invention is to provide a fault indicator with voltage inrush restraint and/or current inrush restraint for overhead applications and with current inrush restraint for underground applications.
Another object of the present invention is to provide a fault indicator that automatically configures its response time to a fault condition for the appropriate overhead or underground application.
A further object of the present invention is to provide a fault indicator that automatically configures activation of its display for the appropriate overhead or underground application.